What is the true form (words) of the koan about one hand clapping? Is it Two hands clap and there is no sound, what is the sound of one hand? Or Two hands clap and there is a sound, now what is the sound of one hand? Or Two hands clap and they make a sound what is the sound of one hand? Not sure.

I'd like to know what it is. I want to do this koan because I want something to think about especially during meditation.

It is relatively easy to accomplish the important matter of insight into one’s true nature, but uncommonly difficult to function freely and clearly [according to this understanding], in motion and in rest, in good and in adverse circumstances. Please make strenuous and vigorous efforts towards this end, otherwise all the teachings of Buddhas and patriarchs become mere empty words. - Torei

I'd like to know what it is. I want to do this koan because I want something to think about especially during meditation.

This looks like a common version: 両掌相打って音声あり、隻手に何の音声かある。

1Myriad dharmas are only mind.
Mind is unobtainable.
What is there to seek?2If the Buddha-Nature is seen,
there will be no seeing of a nature in any thing.3Neither cultivation nor seated meditation —
this is the pure Chan of Tathagata.4With sudden enlightenment to Tathagata Chan,
the six paramitas and myriad means
are complete within that essence.

This koan seems not so effective for western practitioners. It easily creates thoughts from rational judgement.
If it can be thought and answered in any logical ways, it is not considered an effective koan.

The 'one hand clapping' koan, in particular, has unfortunately become something of a cultural cliche. These kinds of ideas were introduced into Western culture in the mid-20th century in popular books and the like, and since that time have become emblematic of the 'mysterious East', used to convey the supposedly paradoxical nature of Zen. But since then Zen has come to mean all kinds of things - if you type 'Zen of...' into the Amazon Search bar, this is what you see:

Zen Of.....png (30.36 KiB) Viewed 610 times

But the point is, koans such as ‘one hand clapping’ are not supposed to 'make sense'. They're not logical syllogisms or rational proofs. Koan practice is an element of specific Zen (and Ch'an) training, and are generally something which are given to students in the context of that training. The fact that they are communicated from teacher to student is key, as the teacher is the one who ascertains if the student really has an insight into the koan. That is the context in which such a koan is meaningful. But even the teacher's judgement is not formularised; there's no 'correct answer'. So, really, trying to explain 'what it's about' or 'what it means', misses the whole point; they are part of an entire context of practice and training, and to really start to understand them, requires studying Zen in depth.

"There is the sound of both palms hit together, but what is the sound of one hand?"

1Myriad dharmas are only mind.
Mind is unobtainable.
What is there to seek?2If the Buddha-Nature is seen,
there will be no seeing of a nature in any thing.3Neither cultivation nor seated meditation —
this is the pure Chan of Tathagata.4With sudden enlightenment to Tathagata Chan,
the six paramitas and myriad means
are complete within that essence.

"There is the sound of both palms hit together, but what is the sound of one hand?"

Koans do not necessarily obviate a logical response although that would probably miss the point. They are intended to get dialog with a teacher going and to point to spiritual insight (which is indeed held by most to be beyond strictly linear reasoning). Here are some visuals not themselves intended as a response in an interview.

"Even if you practice only for an hour a day with faith and inspiration, good qualities will steadily increase. Regular practice makes it easy to transform your mind. From seeing only relative truth, you will eventually reach a profound certainty in the meaning of absolute truth."
Kyabje Dilgo Khyentse Rinpoche.